Offer a writable database location instead of failing the openHEADmain

`ida-tui /bin/ls` asked IDA to create /bin/ls.i64, which a normal user
cannot write, and what came back was the backend's account of it:

    idalib worker launcher 2425195 exited with status 1
    [ida-nexus] Failed to open database /usr/bin/ls

after a full analysis wait, naming neither the file it could not create
nor the reason. Nothing in the message points at permissions, and there
was no way forward from it.

idatui/idbpath.py answers the question before anything is opened: where
would the database go (mirroring ida_nexus's own derivation), can it go
there (os.access only — the pre-flight check must not create files), and
where instead. The proposal is stable per binary
(~/.local/share/idatui/db/<name>-<sha1(realpath)[:8]>.i64) so reopening
the same binary resumes the same names and comments, and hashed so two
busyboxes from different directories cannot collide. DATA_HOME rather
than CACHE_HOME on purpose: an .i64 holds the whole session, and cache
directories are something cleaners may empty.

The answer becomes NexusClient(output_database=...) — the option project
mode already uses to keep everything in its sidecar. `--idb PATH` (also
forwarded by `pane spawn`) says where without being asked. An RPC-driven
TUI is never asked: `pane spawn` polls for ready and would sit out its
whole timeout in front of a modal nobody can answer, so it relocates and
says so in the status line. A failed open re-offers relocation after a
real create probe, since os.access does not know about ACLs, a lying
network mount or a full disk.

tests/test_idbpath.py (pure, 32 checks) pins the path arithmetic, the two
properties of the proposal and that neither check touches the user's
directory; tests/test_idb_relocate_ui.py (textual, no worker, 24 checks)
drives the dialog, Esc, an edited path, the untouched common case, --idb,
the RPC path, and that output_database actually reaches the client.
Verified end to end against a real /bin/ls: 400 functions, and a rename
saved in one session comes back in the next.

0 files changed, 0 insertions, 0 deletions